The present invention relates to a method of installing cables in cable ducts by means of installation devices arranged for exerting a propelling force on the cables. In particular, the invention relates to a method of installing cables by means of installation devices which are provided with a motor and drive wheels for pushing cables into ducts. The present invention also relates to devices for installing cables using a method of this kind. A method and device of this kind are known from European Patent EP 0 292 037 (Reference [1]).
In said European Patent, a method and a device are disclosed for installing cables by means of a combination of propelling forces, a first force being exerted by motor-driven wheels and a second force being exerted by fluid drag. Said Patent also mentions the use of a plurality of such devices for installing cables over longer distances (so called "tandem use").
In prior art techniques, such as disclosed in Reference [1], each installation device is directly coupled to a source of pressurized fluid, such as a compressor. That is, as many compressors as installation devices are required. This is, however, disadvantageous for various reasons. Firstly, installation devices are often used in places where the presence of the compressor poses practical problems, e.g. in narrow streets or in small installation pits. Secondly, a number of installation devices are often required to install cables over considerable lengths, so that the same number of compressors (or other sources of pressurized liquid) are required to install the cable, thus substantially increasing the cost of the method. As each compressor usually requires an operator, labor cost may also be substantial when installing cables over longer distances. Thirdly, moving a compressor to a new location when e.g. an extra compressor is required, is cumbersome, as compressors are generally heavy and difficult to relocate.
For example, the method of Reference [1] may require four installation devices and thus four compressors to install a cable over the length of 2 km.
Other prior art techniques, such as disclosed in e.g. References [5] and [6], do not solve these problems. Reference [5] teaches to relocate the compressor to inject air at another air inlet of the duct as the cable installation proceeds. Similarly, Reference [6] discloses a method in which compressed air is fed into a duct at successive feed ports. This also requires a displacement of the compressor or the use of a plurality of compressors. Moreover, these References do not deal with cable installation using two or more installation devices capable of mechanically exerting a pushing force on the cable, e.g. by means of drive wheels.